1. Field
The present invention relates to a data storage system which is applied to a computer system, and comprises volatile (e.g. SRAM, SDRAM) and nonvolatile (e.g. flash memory, mechanical hard disk) storage components.
2. Description of Related Art
In a conventional computer system, a hard disk drive (HDD) is used as an external memory device wherein a magnetic disk is used as a storage medium. The HDD can be used as a large-capacity file apparatus. However, as compared to a main memory comprising a semiconductor memory (e.g. a DRAM), the access speed of the HDD is lower. A cache system for the HDD has been known as a means for increasing the access speed of the HDD. Dynamic random access memory (DRAM) and flash memory have been used to implement a cache system for the HDD. However, the translation from logical address to physical address format suitable for accessing flash memory and a HDD consume resources of the host computer and affects performance. Accordingly there is a need for a hybrid storage system wherein the performance is improved through elimination of host intervention.
Enterprise-level storage systems typically use arrays of hard disk drives (HDD) as mass storage units, or configured as RAID systems. Data users or clients access the data using standard block-based IO interfaces or over the network using standard file-based access protocols. The HDD array data is managed by dedicated host computers that run storage management applications. As several interface controllers are employed in both host and client systems, enterprise-level storage systems will benefit from a controller architecture that integrates block-based access and file-based or random access to the data. The integration of data transfer controllers for different interfaces in the previously mentioned hybrid storage system that implements multi-tiered caching system for a HDD will extend the benefits of HDD data caching to HDD array systems.